Irene Noblette, later Irene Ryan, is listed as Eileen J. Noblitt on the 1920 census, living in San Francisco with her widowed mother Katie and her sister Annie and brother in law Virgil Wilkerson/Wilkenson.

The 1930 census shows a widowed Anna Wilkerson living in her mother Catherine Noblitt's household, along with a divorced Seth Thompson. The assumption is that the Anna Thompson buried with Irene Ryan is Anna Noblette Wilkerson Thompson, who later married the Seth Thompson in the household, but I haven't found any documentation.

Find a grave- http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=thompson&GSfn=anna&GSbyrel=all&GSdyrel=all&GSob=n&GRid=22832& Notes her as Irene's sister.

Eileen J Noblitt is a listing in the 1920 Census -http://content.ancestry.com/iexec/?htx=View&r=an&dbid=6061&iid=CAT625_142-0011&fn=Eileen+J&ln=Noblitt&st=r&ssrc=&pid=112424046With mother Katie, as immigrant, and Sister Anna Wilkenson, of the right age, and born in KS

The newspaper article Judy dug up pretty well confirms my suspicion that the two women were sisters. Based on Anna's entry in California Death Records, we can conclude that their mother's maiden name was McSharry.